1. Field of the Invention
The present invention relates generally a method and apparatus for photolithographic semiconductor processing and more particularly to method and apparatus for depositing photoresist films.
2. Description of the Relevant Art
Deposition of plasma polymerized methylsilane (PPMS) photoresist layers has been described in: an article by Weidman et al. entitled "New photodefinable glass etch masks for entirely dry photolithography: Plasma deposited organosilicon hydride polymers", published in Applied Physics Letters, Vol. 62, No. 4, 25 Jan. 1993, pp. 372-374; U.S. Pat. No. 5,439,780 to Joshi et al.; and an article by Weidman et al. entitled "All Dry Lithography: Applications of Plasma Polymerized Methylsilane as a Single Layer Resist and Silicon Dioxide Precursor" published in Journal of Photopolymer Science and Technology, Vol. 8, No. 4 (1995), pp. 679-686. As described in these references, a PPMS film having an amorphous organosilicon hydride network structure is deposited by plasma polymerization of a methylsilane precursor gas. When the PPMS film is exposed to UV radiation in the presence of an oxidant such as ambient air, exposed portions of the PPMS film undergo photo-oxidation to form a glasslike, siloxane network material (PPMSO). The resulting patterns can be developed utilizing chlorine plasma etching to provide negative tone patterns. Optionally, the developed pattern may be further oxidized and annealed to convert the remaining material to a hard oxide suitable for further processing. Advantageously, the deposition, development, patterning, and etching steps may all be performed in the gas phase, i.e., using dry plasma processing techniques.
For use in commercial processes, a PPMS film is required to have: (a) good stability, (b) high photosensitivity; and (c) a high deposition rate. Stability of a photoresist film relates to its resistance to degradation of exposure and processing characteristics when the film is exposed to oxidants such as ambient oxygen after the film is removed from a deposition chamber. Typically, in commercial processes the film may not be developed immediately after exposure. Thus, if the film is not stable, the exposed pattern will degrade before the film is developed. Photosensitivity of the photoresist film is the exposure dose ( measured, for example, as mJcm.sub.-2) required to develop patterns that are useful in subsequent pattern transfer steps. High photosensitivity is required in commercial processes so that a short exposure time can be utilized for each substrate. Lastly, deposition rate of the photoresist film (measured, for example, as .ANG./min) is the rate of increase of the film thickness during deposition. High deposition rates are required for high throughput.
The processes for depositing PPMS films disclosed in the above-identified references are not suitable for commercial use. Specifically, the references disclosed PPMS film deposition at low (ambient) temperature and at low (approximately 500 mTorr) pressure to avoid deposition of particles. However, the disclosed deposition rates at the low temperature and pressure are too low for commercial processes that require high wafer throughput.
Thus, in light of the above, there is a need in the art for commercially useful method and apparatus for depositing PPMS film.